Method for making rayon filaments



m FOR AKIN RAYON Hm l'ilod m 4. 1962 vi'scosE 1-207 ueous formola uyde VISCOSE and 'HCHO Prompt Extrusion into Acid Spin Both Fl LAME NTS Stretching STRETCHED F ILAMENTS mvenfarg Elms K/e/n Dona/d SA/e/soq Basil E M. Bmgham 5y Meir attorneys METHOD FOR MAKING RAYON FILAMENT S Elias Klein, Mobile, Donald S. Nelson, Eight Mile, and

Basil E. M. Bingham, Mobile, Ala., assignors to Courtaulds North America Inc., a corporation of Filed\May 4, 1962, Ser. No. 192,322 7 Claims. (Cl. 18-54) This invention relates to a method for themanufaoture of rayon filaments by the viscose process andin particular to an improved process by means of which high tenacity filaments can be made more easily than has hitherto been possible. I

The effort to obtain ever higher tenacities in rayon fibers has recently become intense. ago tenacities of 2.425 g./den. were considered very good for textile purposes, today textile'fibers having over 4 g./den. are being marketed and there is a demand for even higher tenacities.

Various manufacturing techniques are recognized in the art as leading to increased. tenacities.

One particularly useful technique is to start with a cellulose having a high degree of polymerization, and prepare and spin the viscose under conditions such that degradation of the celluloseis avoided to the greatest degree possible. In general these conditions involve xanthating the alkali cellulose without substantial ageing and spinning the viscose, unripened, at a very high gamma value into a spinning bath low in acid and salt (Na SO and containing substantially no zinc. The filaments thus formed are stretched to a very high degree (150350%) while incompletely regenerated, regeneration being completed during or after stretching.

Fibers made in accordance with this process have a crystallinity of say 5060%. They have a substantially circular cross section, a smooth, non-crenulated surface and no discernible skin-core structure.

In the manufacture of such filaments and indeed in making most high tenacity filaments it is desirable to stretch the filaments to the maximum degree possible. If, however, regeneration of the filaments is largely accomplished before stretching, the amount of stretch which canbe applied .is not great. To increase the amount of stretch which can be applied various regeneration retardants have been added to the spinning bath, and among these is formaldehyde.

Formaldehyde for many purposes is a superior re tardant to others which have been proposed; for example, it avoids the condensed filaments which are obtained using zinc salts.

The use of formaldehyde in the spinning bath is not without drawbacks, however. While the concentrations used are not great (usually 5%, maximum), they are sufficient to give rise to a substantial loss of formaldehyde overhead. This represents waste, but what is perhaps more important, it causes discomfort and in some cases raises a real health hazard for the operators. Moreover, the formaldehyde reacts with the xanthate sulfur decom position products to form, inter alia, trithiane, an insoluble material which must be continuously removed from the spinning bath.

It has been proposed to add formaldehyde to the viscose, rather than to the spinning bath, with the thought that by putting the formaldehyde in intimate asociation with the cellulose, less formaldehyde could be used and some of the problems accompanying its use in the bath, avoided. Under the conditions proposed, however, formaldehyde when added to the viscose was not very effective in retarding regeneration, and any improvement observed over a period of time was due chiefly to the formaldehyde While a few years.

1000. The viscose may be ripened 3,109,700 Patented Nov. 5, 1963 ice carried into the spinning bath and the resulting build-up of the formaldehyde concentration in the bath. Moreover, it was found that when formaldehyde was added to the viscose, it caused a substantial reduction in gamma value, thus upsetting the entire spinning system. This was a particularly serious obstacle in the formation of the highly crystalline high tenacity fibers referred to above, since obtaining these fibers depcn s on the use of substantially unripened, high gamma value 'viscose.

In accordance with the invention theseg difliculties are overcome, and a process is provided by means of which very small quantities of formaldehyde, added to the vis cose, can be used effectively to retard regeneration.

, The present invention is based upon two discoveries:

First, that the state of polymerization of the formaldehyde has a direct bearing on its effectiveness as a regeneration retardant, and specifically that monomeric formaldehyde is the effective agent in this respect; and

Second, that the effect of added formaldehyde on the gamma number of the viscose is related to the residence time of the formaldehyde in the viscose.

The invention therefore comprises, in a first aspect, a process for the manufacture of rayon filaments wherein viscose is extruded into an acid spinning bath to form filaments and the filaments are stretched, characterized in that formaldehyde in substantially monomeric form is mixed with the viscose prior to spinning.

In a second aspect the invention comprises a process for the manufacture of rayon wherein viscose is extruded into an acid regenerating bath and subsequently stretched, and characterized in that formaldehyde is added to the viscose just prior to spinning.

Preferably these two improvements are used together, i.e. a solution of monomeric formaldehyde is injected into the viscose just prior to spinning.

The drawing illustrates an embodiment of the invention wherein the two improvements are used together.

THE V'ISCOSE The invention is, of course, of general applicability in that it can be employed in any viscose process where a high degree of stretch is to be applied to the newly spun filaments. Thus the viscose, in the most general aspect of the invention, may have from 1 to say 10% cellulose, and 2 to 10% NaOH. The degree of polymerization of the cellulose in the viscose may range from say 200 to [salt figure (NaCl)=4 to 12] or unripened [SF 13 to 23] and may have a gamma value of say 45 to 95. viscosity at spinning may range from 20 to 450 seconds (ball fall), preferably 30-400. In accordance with the invention, at the time of spinning it will contain between about 0.2 and about 1.5% formaldehyde.

As pointed out above, however, the invention is of particular use in connection with the production of highly crystalline high tenacity filaments and in the manufacture of such filaments, the viscose will normally contain 2 to 6% cellulose, and 2 to 8% NaOH. ilt will be substantially unripened, SF=l5 to 23, :60 to 95. The cellulose Will preferably be of high DP (say 350 to 1200) and the viscose will have a viscosity of say 30 to 250 seconds (ball fall). In accordance with the invention, the viscose will contain, just prior to spinning, between about /2 and about 1% formaldehyde.

THE FORMALDEI-IYDE As noted above the formaldehyde should] be in substantially monomeric form. In this connection it is pointed out that the polymerization of formaldehyde in aqueous solution is (within presentterms of reference) reversible, and the degree of polymerization is a direct function of concentration. In normal 37% formalin, for example,

less than one-third of the total formaldehyde is present as monomer. This proportion may, however, be increased by simply diluting the solution. Thus, in a 2.4% aqueous HCHO solution 98% of the formaldehyde is present as monomer.

In general the concentration of the formaldehyde solution added to the viscose should be between about 1 and about 20% by weight, preferably between about 2' and about 6% by weight. Under these conditions between about 99 and about 70, preferably between about 99 and about 90% of the formaldehyde will be in mono-.

meric form.

"It should be pointed out that in the present process, it

is not possible to rely on the dilution of a standard comaldehyde to the viscose may be any of those conventionally used in the art to introduce other additives. The formaldehyde may be added to the viscose batchwise in a suitable mixing device and agitated vigorously, or in order to cut down the residence time of the formaldehyde in the viscose, the techniques used for injecting pigment solutions into viscose may be employed.

The residence time of the formaldehyde in the viscose should be kept as short as possible. The minimum time will depend on spinning conditions. The purpose of using formaldehyde is to retard regeneration, i.e. to prevent a decrease in gamma number, in the spinning bath. If, however, the residence time for the formaldehyde in the viscose is such as to cause a decrease in gamma number before spinning, which is equal or greater than the retarding effect obtained in the spinning bath, the advantage of the formaldehyde is lost. This ultimate limit is usually reached with a residence time on the order of two hours. However, it is preferred to spin with a residence time of not more than 90 min., say 10 to 60 minutes.

SPINNING CONDITIONS In its broadest application the invention envisions spinning viscose containing monomeric formaldehyde into any of the acid spinning baths hitherto employed in the art. This, the bath may contain from say 3 to 10% H 80 from 6 to 23% Na SO and from to 6% ZnS0 Other components such as MgSO and the organic coagulation modifiers such as polyethylene glycol, may also be present in the bath, and the latter may be present in the viscose. The bath may have a temperature between say 15 C. and 50 C. The viscose may be spun at an extrusion ratio of say 0.2 to 1.5, with a bath travel of say 3 to 25 inches.

More particularly,'the invention will be used in the production of high tenacity filaments as indicated above. In this case the viscose is spun into a bath containing 3 to 7% H 80 6 to 18% Na S0 and less than 0.1% ZnSO The bath may have a temperature from say 15 to 30 C. The viscose is spun at an extrusion ratio of from about 0.3 to about 0.6.- A bath travel of say 3 to 10 inches is used.

STRETOHIN G At some point after the filaments have acquired sufficient strength, but before regeneration is completed, the filaments are stretched. This may be carried out in the spinning bath itself, in a secondary acid bath, in a water bath, in stream or in air. The degree of stretch applied will, of course, vary with the nature of the process, but will in general be between about 40% and about 350%.

When the high tenacityhighly crystalline filaments referred to above are being made, the filaments will be removed from the spinning bath before they are more 4 than regenerated and stretched, preferably in hot water or steam (see the copending applications of Klein, Serial No. 184,510, filed April 2, 1962, and Richardson, Serial No. 191,004, filed April 30, 1962, both assigned to the assignee of the present application), by between about 150% and about 350%.

SUBSEQUENT PROCESSING Following stretching, the regeneration of filaments can be completed, if it has not already been completed during stretching. The filaments can be washed and desulfurized in the conventional way and can be cut up into staple either before or after these treatments.

In the drawing, 1 to 20% aqueous formaldehyde is added to viscose promptly before extrusion into anacid spin bath, and the freshly extrusion-formed filaments are stretched.

The invention will be further described by means of the following specific examples which are given for illustration only and are not to be taken as in any way limiting the invention beyond the scope of the appended claims.

Example I To illustrate the effect of formaldehyde on the ripeness of viscose, a viscose containing 5.91% cellulose and 5.98% NaOH, having a ball-fall viscosity of 364 seconds, a salt figure of 20.4 and a gamma value of 63.1 was mixed with an equal weight of 1.8% aqueous formaldehyde (98% monomer), under reduced (25 mm. Hg)vpressure. At intervals after mixing had begun the salt (NaCl) figure was determined. Theresults were as follows:

Time after mixing Salt figure 0 20.4 1 35 minutes 19.9 2 hours 17.4 3 hours 15.2 4 hours 13.8 4.5 hours (13.8

By way of comparison equal weights of the same viscose and water (no formaldehyde) were mixed. After 4.5 hours the salt figure was 20.2.

Thus it will be seen that the presence of formaldehyde has a very pronounced effect on the salt figure.

A sample of the viscose after 35 minutes storage was spun into a bath containing 7.26% H SO and about 8% Na SO (no zinc). It was stretched'the maximum amount possible, 260%, in a secondary bath containing less than 0.1% H SO at -90 C. The filaments obtained had a dry tenacity of 5.28 g./den., a dry elongation of 6.8%, a wet tenacity of 3.96 g./den. and a wet elongation of 7.4%.

For comparison, a sample of the viscose aged 4.5 hours was spun into a bath having less regenerative power, the H280 concentration being 3.77% and the Na SO 8%. The maximum stretch possible (using the same stretch conditions as before) was The filaments had a dry tenacity of 3.51 g./den., a dry elongation of 5.5%, a wet tenacity o'f 2.89g./den. and a wet This viscose was diluted with an aqueous solution con taining 4.46% formaldehyde (approximately 92% mono- To compensate for the expected decrease in gamma number.

mer) to give a viscose containing 5.06% cellulose and 0.75% formaldehyde. It was spun after 35 minutes of mixing at which time its salt figure was 20.5. The spinning bath contained 5.05% H 80 8% Na SO and no zinc. It was at a temperature of 23 C. ,The filaments were stretched about 165% (less than the maximum possible) in a water bath at 8090 C.

The average filament dry tenacity was 4.99 g./den.

In a parallel experiment, the same viscose was diluted with water and formalin (37% HCHO) was added to give 5 .06% cellulose and 0.73% formaldehyde. This was spun, as before, at a salt figure of 20.5 and stretched 197%. The dry tenacity was 4.31 g./den.

Example III Example IV Samples of a viscose containing 3% cellulose, 3.8% NaOH and 1% HCHO, of which about 93% was in monomeric form, were spun at different times after the addition of the formaldehyde into a bath containing 5% H 80 8% Na SO and no zinc. The filaments were stretched to the maximum degree, washed and dried. The tenacity of the several samples was then measured. The results are tabulated below:

Time alter HCHO addition (min.) 45 30 210 300 Stretch percent (maximum obtainable) 172 77. 5 63 58 Tenacity, dry (g./den.) 4. 24 2. 54 1. 80 1. 38

A control sample, without formaldehyde, had a dry tenacity of 2.51 -g./den.

We claim:

1. In a method for the manufacture of rayon filaments wherein viscose is extruded into an acid spinning bath 6 to form filaments and said filaments are stretched, the improvement which comprises mixing an aqueous solution containing between about 1 and about. 20% formaldehyde with said viscose not more than two hours prior to spinning, said formaldehyde being in substantially monomeric form when added to said viscose.

2. The method claimed in claim 1 wherein the formaldehyde is added to the viscose as an aqueous solution containing between about 2 and about 6% formaldehyde.

3. The method claimed in claim 1 wherein the formaldehyde is added not more than 90 minutes prior to spinning.

4. In a method for the manufacture of rayon filaments in which viscose is extruded into an acid spinning bath to form filaments and said filaments are stretched, the improvement which comprises adding an aqueous solution containing between about 1 and about 20% formaldehyde to said viscose just prior to spinning.

5. In the manufacture of high tenacity rayon filaments wherein an unripened-viscose is extruded. into an acid spinning bath low in regenerating power, and is stretched by at least 150% prior to regeneration, the improvement which comprises injecting a dilute aqueous solution of formaldehyde containing between about 1 and about 20% formaldehyde into said viscose immediately prior to spinning, thereby retarding regeneration of said filaments.

6. The method claimed in claim 5 wherein the formaldehyde is at least 70% monomer.

7. Viscose having a gamma number between and 95 and containing between about 0.5 and about 1% formaldehyde, at least of said formaldehyde being monomeric.

References Cited in the file of this patent UNITED STATES PATENTS 2,942,931 Mitchell et a1 June 28, 1960 3,018,158 Mitchell et al. Jan. 23, 1962 3,026,169 Eskridge Mar. 20, 1962 3,026,170 McPeters Mar. 20, 1962 FOREIGN PATENTS 626,141 Canada Aug. 22, 1961 

1. IN A METHOD FOR THE MANUFACTURE OF RAYON FILAMENTS WHEREIN VISCOSE IS EXTRUDED INTO AN ACID SPINNING BATH TO FORM FILAMENTS AND SAID FILAMENTS ARE STRETCHED, THE IMPROVEMENT WHICH COMPRISES MIXING AN AQUEOUS SOLUTION CONTAINING BETWEEN ABOUT 1 AND ABOUT 20% FORMALDEHYDE WITH SAID VISCOSE NOT MORE THAN TWO HOURS PRIOR TO SPINNING, SAID FORMALDEHYDE BEING IN SUBSTANTIALLY MONOMERIC FORM WHEN ADDED TO SAID VISCOSE. 